Highly plasticized vinyl resin films, and in particular, plasticized polyvinylchloride films and substrates, have been used in a variety of applications. These vinyl substrates may contain as much as 25 to 75 parts of plasticizer to 100 parts of vinyl resin. There is a tendency, however, for the plasticizers to migrate to the surfaces of the vinyl films. One of the problems that has been observed with polyvinyl films, and in particular, cast polyvinyl films, has been the formation of mottle on the surfaces of the vinyl films. Mottle is defined as the presence of matte regions on an otherwise glossy film surface. This problem makes the product aesthetically unattractive in many applications. The problem of mottling is particularly evident and visible in dark-colored films. The development of mottle on vinyl films is a particular problem when the vinyl films are to be used in the preparation of signs and high-end striping.
Mottling has been observed to develop, for example, in cast vinyl facestock when a pressure-sensitive construction containing such facestocks is wound from a roll or is removed from a stack of sheets, and this mottling detracts from the desired uniform glossy appearance of the surface. It has been suggested that the mottling develops as a result of the migration of the plasticizer contained in the highly plasticized vinyl film, and this migration is apparently promoted and enhanced by contact of the vinyl surface with rough porous surfaces such as, paper, film and polycoated release liners which are used in conjunction with the vinyl films when preparing composites.
The problem of plasticizer migration in composites has been previously recognized. For example, U.S. Pat. No. 4,284,681 discloses a composite material having a highly plasticized layer, a fibrous backing layer, and an intermediate plasticizer barrier layer such as polyurethane resin between the polyvinylchloride layer and the fibrous backing. The barrier layer directly contacts the polyvinylchloride layer and is disclosed to reduce migration of plasticizer in the highly plasticized polyvinylchloride layer to or through the backing layer. The composite can be bonded using an adhesive to walls, floors and/or ceilings and is reported to be effective to reduce dust and/or bacteria in the area. The dust and/or bacteria adhere to the exposed surface of the highly plasticized polyvinylchloride layer from which they can be removed by washing.
U.S. Pat. No. 4,045,600 discloses a process in which successive layers of a polyurethane resin are applied directly to a plasticized polyvinylchloride substrate for the purpose of inhibiting plasticizer migration. An object of the process described is a reduction in the tackiness of the surface of the plasticized polyvinylchloride. The patentee describes various polymeric coatings for plasticized polyvinylchloride substrates including acrylic ester polymers, polyvinylacetate, and modified polyamides.
U.S. Pat. No. 4,605,592 describes a multilayer decorative article having, in order, an ink-receptive vinyl film layer, a plasticizer barrier layer and a pressure-sensitive adhesive layer. The adhesive layer is adapted to maintain adhesion to highly plasticized vinyl substrates, and the intermediate barrier layer is reported as being capable of preventing plasticizer from migrating from the vinyl substrate into the vinyl film outer layer. Among the barrier film materials described in the '592 patent are aliphatic polyurethane resins. In addition, the adhesives utilized in the composite are designed to be plasticizer-resistant.